Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A WOUND DRESSING
Field of the Invention
The present invention relates to an impregnated wound dressing having an
outer membrane overlay layer and to a method of production thereof. In
particular the dressing comprises a core layer that has been impregnated with
a wound healing agent, such as honey, and an outer membrane overlay layer.
Background
Wounds impact on the lives of many people. Some individuals suffer from
non-healing wounds such as ulcers, infected wounds, inflamed wounds and
the like. Wound dressings are needed to protect such wounds from further
infection. Some wounds discharge (exude) moisture or fluids and for such
wounds a wound dressing needs to be absorbent to contain the exudate while
the wound dressing is in situ.
Wound dressings are often impregnated or coated with agents that facilitate
wound healing or that reduce the chance of infection. Such agents include,
but are not limited to, silver products, antimicrobial products such as
antibiotics or honey or honey extracts or anti-inflammatory agents or
products.
The main reasons for the application of a dressing are to facilitate and
accelerate healing of a lesion; to prevent malodour; to minimise pain; to
prevent and counteract infection; to absorb exudate and to reduce scar tissue.
Wound dressings that are impregnated with the likes of a cream or honey can
be sticky or tacky in nature and can be difficult to handle when extracting
the
dressing from its packaging and placing on a wound. There is a need to
provide an impregnated wound dressing that is dry to the touch, that does not
adhere to the wound bed while still allowing a flow of exudate into the
dressing, that is easy to manufacture and package and not difficult to apply
to
a wound.
The applicant produces a honey impregnated wound dressing that is
described in PCT/GB2009/001407, the contents of which are incorporated
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herein in its entirety. The preferred manufacturing embodiment described in
PCT/GB2009/001407 includes the step of dusting the impregnated core layer
with a carboxymethylcellulose (CMC) layer. It has been found that during the
dusting step involved in the manufacturing process it can be difficult to
achieve a uniform thin layer of CMC dusted over the impregnated core layer.
The object of the present invention is to provide a wound dressing that
overcomes the abovementioned difficulties or to at least provide the public
with a useful alternative.
Summary of the Invention
In a first aspect the invention provides a wound dressing including a core
layer
impregnated with a wound healing agent and at least one outer membrane
overlay layer.
In one embodiment the membrane overlay layer is selected from a cured
carboxymethylcellulose layer, a silicone comprising layer, a
polytetrafluoroethylene comprising layer, a silicone and
polytetrafluoroethylene comprising layer, and a cross-linked polyurethane
layer or combinations thereof.
In one embodiment the membrane overlay layer comprises a cured
carboxymethylcellulose layer.
In one embodiment the carboxymethylcellulose is sodium
carboxymethylcellu lose.
In one embodiment the membrane overlay layer further comprises a
plasticizer.
In another aspect, there is a method of producing a wound dressing as
defined above, the method including the step of impregnating a core layer with
a wound healing agent and then overlaying at least one surface of the
impregnated core layer with a membrane overlay layer.
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In one aspect there is a method of treating a wound, including the step of
placing a wound dressing having a membrane overlay layer as defined above
on a wound to facilitate the healing of the wound.
Additional aspects and embodiments of the invention will be apparent from the
description and Figures that follow.
Definitions
The term a "membrane overlay layer" as used herein is understood to mean a
pliable sheet-like structure acting as a boundary between the core layer of
the
wound dressing to which the membrane overlay layer is applied.
The term" a wound healing agent" as used herein is understood to mean a
liquid, cream or a gel that is impregnable into a core layer and includes,
honey, gels or liquids of silver products, antimicrobial products such as
antibiotics or honey or honey extracts or anti-inflammatory agents or products
that promote wound healing or promote wound closure.
Brief description of the drawings
The invention will now be described by example only with reference to the
figure where:
Figure 1. shows a cross-sectional view of a wound dressing of the present
invention having a core layer impregnated with a wound healing agent, which
core layer is sandwiched between two membrane overlay layers.
Detailed Description
With reference to Figure 1, in a first aspect the invention provides a wound
dressing including a core layer 1 impregnated with a wound healing agent and
at least one outer membrane overlay layer 2. In the embodiment illustrated
the core layer 1 is sandwiched between two membrane overlay layers 2.
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In one embodiment the membrane overlay layer is selected from a cured
carboxymethylcellulose layer, a silicone comprising layer, a
polytetrafluoroethylene comprising layer, a silicone and
polytetrafluoroethylene comprising layer, and a cross-linked polyurethane
layer or combinations thereof.
In one embodiment the membrane overlay layer comprises a cured
carboxymethylcellulose layer. In one embodiment the carboxymethylcellulose
is sodium carboxymethylcellulose.
In one embodiment the membrane overlay layer further comprises a
plasticizer. In one embodiment the plasticizer is selected from glycerin,
polyethylene glycol, propylene glycol, monoacetin, triacetin, triethyl
citrate,
sorbitol, 1,3-butanediol, D-glucono-1,5-lactone, and combinations thereof.
In one embodiment the plasticizer is glycerin.
In one embodiment the membrane overlay layer comprises a cured
carboxymethylcellulose-glycerin layer.
In one embodiment the membrane overlay layer comprises a cured sodium
carboxymethylcellulose-glycerin layer.
In another embodiment the membrane overlay layer comprises a blend of
silicone and polytetrafluoroethylene.
In one embodiment the membrane overlay layer is between about 0.1pm -
2.0mm in thickness. In another embodiment the overlay layer is between
about 0.5prn -1.0mm in thickness.
In one embodiment the membrane overlay layer does not absorb any of the
wound healing agent impregnated into the core layer.
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In one embodiment the core layer is a superabsorbent material. In another
embodiment the superabsorbent material is a superabsorbent polymer fibre,
such as a cross-linked polyacrylate fiber marketed as Oasis SAF TM or SAFTM.
In one embodiment the core layer comprises an alginate. It is to be
appreciated that any one of the alginate dressings in Table 1, could be
impregnated with a wound healing agent, such as a honey and then coated
with at least one membrane overlay layer, such as a cured carboxyrnethyl
cellulose layer.
Table 1
Manufacturer Brand name Dressing
ConvaTec AQUACEL Alginate absorbent dressing
ConvaTec AQUACEL Ag Burn Alginate absorbent dressing
ConvaTec AQUACEL 0 Extra Two layers of Hydrofibere
technology in
a dressing
3ivi TM Tegaderm TM Alginate Silver absorbent dressing
3M Health Care Tegaderm TM High gelling Alginate wound dressing
Alginate dressing
3M Health Care Tegaderm TM High Integrity Alginate wound dressing
Alginate dressing
Derma Sciences, Inc. AlgiCell 0 Alginate wound dressing
Smith & Nephew, Inc. ALGISITE Calcium alginate wound dressing
Coloplast Corp Biatain 0 Alginate Ag Alginate dressing with silver
Dressing
Coloplast Corp Biatain 0 Soft Alginate Alginate dressing
Dressing
McKesson MedicalSurgical Calcium Alginate Rope Dressing
Calcium Alginate Sheet Dressing
DermaRite Industries, LLC DermaGinateTM 12" Rope
DermaGinateTM Dressing
MPM Medical, Inc ExcelGinate TM Non-woven calcium alginate dressing
Gentell Wound and Skin Care Gentelle Calcium Calcium alginate dressing
Alginate
DeRoyal Kalginate TM Heavy-fiber alginate dressing
ConvaTec KALTOSTATO Absorbent gel-fiber
KALTOSTAT0 Rope
Covidien Kendall TM Calcium Calcium alginate dressing
Alginate Dressing
Covidien Kendall TM Calcium-Zinc Calcium-Zinc alginate
dressing
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Alginate Dressing
Medline Industries, Inc. Maxorb @ II 100% alginate dressing
Medline Industries, Inc. Maxorb @ Extra Calcium calcium alginate and
sodium
Alginate carboxymethylcellulose fibers
Medline Industries, Inc. Opticell Alginate dressing
MediPurpose , Inc. MediPlusTM Alginate a calcium containing dressing
derived
Dressing from seaweed
Molnlycke Health Care US, Melgisorbe Calcium A calcium
alginate dressing
LLC Alginate Dressing
Hollister Wound Care Restore Calcium Calcium alginate dressing
Alginate Dressing
Hartmann USA, Inc. Sorbalgone An absorbent calcium alginate
dressing
MyIan Bertek Sorbsan0 A calcium alginate dressing
I Pharmaceuticals, Inc.
It is also to be appreciated that the membrane overlay layer may comprise a
silicone comprising layer, a polytetrafluoroethylene comprising layer, a
silicone and polytetrafluoroethylene comprising layer, a cross-linked
polyurethane layer or combinations thereof. The membrane overlay layer is
preferably non-adherent and sterilizable for wound dressing applications. In
some instances it would be appropriate to fenestrate or perforate the
membrane overlay layer to allow for release of the wound healing agent from
the core layer into the wound and the flow of exudate through the membrane
overlay layer in contact with the wound bed, when in use. Such fenestration
or perforation would take place in the wound dressing manufacturing process
once the membrane overlay layer was in situ over the impregnated core layer.
An example of a product that would also be suitable for use as an overlay
layer is SilonTM, which is produced commercially by BioMed Sciences.
SiloflTM comprises a blend of silicone and polytetrafluoroethylene. SilonTM
can
be readily fenestrated, perforated or sliced to interrupt the integrity of the
membrane layer.
In one embodiment the wound healing agent is selected from a honey, a silver
agent, an antimicrobial agent or mixtures thereof.
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In one embodiment the wound healing agent is a honey derived from the
Leptospermum genus. In one embodiment the wound healing agent is a
honey derived from Leptospermum scoparium.
In another aspect, there is a method of producing a wound dressing as
defined above, the method including the step of impregnating a core layer with
a wound healing agent and then overlaying at least one surface of the
impregnated core layer with a membrane overlay layer.
In one embodiment the method includes the step of packaging the wound
dressing between protective liners.
In a further embodiment the method includes the step of packaging the wound
dressing into a sealable pouch package.
In one embodiment the method includes the further step of sterilizing the
dressing. In one embodiment the sterilization step is achieved by gamma
irradiation.
In one aspect there is a method of treating a wound, including the step of
placing a wound dressing as defined above on a wound to facilitate the
healing of the wound.
The examples described herein are provided for the purpose of illustrating
specific embodiments of the invention and are not intended to limit the
invention in any way. It is understood that variations and modifications may
be made without departing from the scope of the invention. Persons of
ordinary skill can utilize the disclosures and teachings herein to produce
other
embodiments and variations without undue experimentation. Furthermore,
where known equivalents exist to specific features, such equivalents are
incorporated as if specifically referred to in this specification. All such
embodiments, variations, and equivalents are considered to be part of this
invention.
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Examples - Manufacture of the dressing.
Example 1: Core Layer is OASIS SAF impregnated with Leptospermum
derived honey.
As described in PCT/GB2009/001407, the manufacture of OASIS SAF by
Technical Absorbents comprises polymerisation in water followed by extrusion
of the aqueous polymer solution in a hot air stream to dry and cure the
polymer, thereby producing insoluble polymer fibres. An extremely high
conversion rate of the raw materials to polymer is achieved. Moisture may be
added to the fibres to aid processing, and the fibres are precision cut into a
range of staple lengths. The OASIS Super Absorbent technology can also be
used to produce filament yarns (OASIS-FIL) and polymer solutions (OASIS-
PS), either of which may be used in the invention. Typically, the thickness of
the SAF layer when in the form of a sheet ranges from 0.25 mm to 10 mm; for
example, the sheet may be 0.5mm, 1 mm, 1.5mm, 2mm, 2.5mm, 3mm,
3.5mrn, 4nnm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mrn, 7.5mrn, &inn,
8.5rnm, 9mm, 9.5mm or 10 mm thick. Preferably, the sheet is less than 5mm,
4mm or 3nnm thick and more preferably less than 2mm thick.
The OASIS SAF fibre product is then impregnated with honey. The honey
may be impregnated by continuous (roll to roll) dip coating. In this method, a
roll of the super-absorbent sheet pre-cut to a desired width is drawn through
an immersion tank of warm honey (typically between 35 C-50 C, for example
35 C-45 C), typically at a constant speed after which it is wound into a roll.
It
is appreciated that the sheet to be impregnated need only be just beneath the
surface in the tank of honey. Blades to remove excess honey are combined
with a nip roller to create a constant pressure at the point of exit from the
tank.
The degree of impregnation of the sheet with the honey is determined by the
submersion time and the time under roller pressure. It is therefore important
to
regulate the honey level within the tank and the time under roller pressure.
The level of honey in the tank is maintained by pumping more honey into the
bath when the level is reduced. Typical dwell times in the honey tank are in
the region of 2-6 seconds depending on the material being impregnated. The
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speed is determined by the tensile strength along the length of the material.
After leaving the tank and passing the nip rollers the impregnated sheet is
dried before being wound into a roll form. The roll is further processed into
cut
lengths for use as a wound dressing. It will be appreciated that other methods
of impregnation may also be used such as, for example, batch process of
emersion.
The superabsorbent material is preferably impregnated with the honey such
that the honey does not saturate the super-absorbent material, thereby
leaving capacity for absorbing lesion fluid components. In any event, it is
appreciated that the super-absorbent material is impregnated with the honey
such that the honey does not utilise all of the super-absorbent material's
capacity to absorb fluid. It is believed that the honey is held by the
superabsorbent fibre material by way of capillary action. The pH of honey is
typically around 3.9-4.3 and the applicant believes that the absorbent
capacity
of the superabsorbent fibres at the typical pH of honey is shut down and that
the fibres do not absorb any of the free water in honey. While it is believed
that the honey coats the super-absorbent material (eg fibres) and reduces the
absorbency rate of the fibres it is further believed that as the honey is
diluted
by wound exudate, the fibres' capacity for absorption is restored, possibly
because the pH of the honey increases as it is diluted.
Preferably, the super-absorbent material is impregnated with honey such that
the super-absorbent material is able to absorb at least 10 times its dry
weight
when in water, and more preferably at least 20, 30, 40 or 50 times its dry
weight. For example, when the super-absorbent material is impregnated with
honey in a weight ratio of 4:1, the super-absorbent material typically absorbs
10 times its dry weight when in water.
The ability of a super-absorbent material to hold honey within its structure
is
dependent on the mass, density and type of the absorbent material used and
the impregnation method used. A typical dosage of honey which does not lead
to saturation is 0.2g/cm2, and so for a 5 cm x 5 cm sheet the dosage would be
5g honey and for a 10 cm x 10 cm sheet the dosage would be 20g honey.
Thus the sheet may contain between 0.1g/cm2 and 0.3g/cm2 such as
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between 0.15 g/cm2 and 3 g/cm2. However, it will be appreciated that other
dosages outside this range may be used which give the required utilisation of
absorbent capacity, depending upon the super-absorbent material used and
the thickness of the sheet.
The membrane overlay layer is prepared by taking a polyester (PET) carrier
film and coating the film with a layer of sodium carboxymethylcellulose
(NaCMC) (99-90%) -and glycerin (up to 10%) Suitable sodium CMC is
commercially available from Hercules, Inc. (Wilmington, DE) under the
AQUALON brand.
The coating is achieved by spraying the NaCMC/glycerin mixture onto the
PET carrier film. It is to be appreciated that other coating systems may be
used for example the Meyer-Bar technique. The PET film is then used to
"carry" the NaCMC-glycerin layer as the PET film and NaCMC-glycerin layer
are infrared radiated to cure the NaCMC-glycerin layer to form a polymeric
layer and to create a CMC cured film that can be subsequently removed from
the PET carrier film. The separated NaCMC-glycerin cured layer can then be
rolled onto at least one surface of the honey impregnated OASIS SAF core
layer described above to prepare a roll of wound dressing of the invention.
The roll of wound dressing can then be cut to produce the desired shape and
size of the wound dressings. The wound dressings can then be placed
between liner layers and pouched to produce a single wound dressing. The
wound dressing would then be sterilized by a process such as by way of
gamma irradiation.
Example 2: Core Layer is OASIS SAF impregnated with Leptosperrnum
derived honey and having a SilonTM coating.
The core layer of Oasis SAF was prepared and impregnated with
Leptospermum derived honey.
A membrane overlay layer was prepared by BioMed Sciences and then
applied by rolling the SilonTM layer onto at least one surface of the honey
impregnated OASIS SAF core layer described above to prepare a roll of
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wound dressing of the invention. SilonTM is an example of a combination
product comprising a blend of both silicone and polytetrafluoroethylene
(PTFE) also known as TeflonTm. The wound dressing was then fenestrated by
feeding the dressing through a cutting tool to slit the SilonTm layer and to
partially slit the core OASIS SAF layer. It is to be appreciated that other
means of perforating the membrane layer would also be possible, such as
passing the dressing by a needle press that presses a plurality of needles
through the dressing to perforate the outer membrane layer. The wound
dressing is then cut to produce the desired shape and size of the wound
dressings. The wound dressing may then be optionally placed between liner
layers and then pouched to produce a single wound dressing. The wound
dressing would then be sterilized by a process such as by way of gamma
irradiation.
The present invention and its embodiments have been described in detail.
However, the scope of the present invention is not intended to be limited to
the particular embodiments of the invention described in the specification.
Various modifications, substitutions, and variations can be made to the
disclosed material without departing from the essential characteristics of the
present invention. Accordingly, one of ordinary skill in the art will readily
appreciate from the disclosure that later modifications, substitutions, and/or
variations performing substantially the same function or achieving
substantially the same result as embodiments described herein may be
utilized according to such related embodiments of the present invention.
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